1. Field of the Invention
This invention relates to a packaging carton blank, a method of making a carton therefrom and a carton made by the method, particularly in respect of the packaging of liquid.
2. Description of the Prior Art
Gable-topped packaging cartons with extensible pouring spouts are conventional. One of the problems with the gable form of top closure is unreliable sealing because of its relatively complicated construction. Reliable sealing thereof becomes even more difficult to attain when the top closure incorporates an extensible spout provided by one of the sub-panels of the loop of upper sub-panels serving to form the sealing fin and one of the sub-panels of the loop of lower sub-panels serving to obturate the carton top, because the spout should be relatively easy to open, yet this requirement is not readily reconcilable with good sealing together of the sub-panels forming the sealing fin.
U.S. Pat. No. 3,270,940 discloses a gable-topped carton which is formed from a blank consisting of paperboard coated on both sides with thermoplastics and in which the middle zones of the internal and external surfaces of the upper sub-panel of such a spout, or each such spout when there are spouts at the respective ends of the top closure, are coated with an adhesive material, for example of the organo-siloxane type. The corresponding parts of the internal surfaces of the two adjacent upper sub-panels may also be coated with the adhesive material. For the purpose of increasing the degree and durability of liquidtightness of the closure, the jaws used in sealing the fin may apply extra pressure to selected areas of the closure parts, producing in the closure plies indentations or embossments which effectively close up incipient liquid escape channels. Such an area is a rectangular embossed area on one of the said two adjacent upper sub-panels and adapted to effect blocking of an incipient channel in the fin along the inner lateral edge of a sealing strip panel extension. The area can be centrally relieved to avoid interference with the spout.
It has been found in practice that, in spite of these measures, the middle zone of the upper sub-panel of the spout may still adhere firmly to the internal surfaces of the two adjacent sub-panels so that the spout cannot be readily opened and thus becomes badly distorted or torn in opening it.